Methods of making non-rigid rotative abrasive structures



y 1958 T. J. MILLER EI'AL 2,843,469

METHODS OF MAKING NON-RIGID ROTATIVE ABRASIVE STRUCTURES Original FiledNov. 7. 1955 INVENTORS fi/EODOREJ Ma 5? ZARA 1. 607/052 MMMQM1477'0RNEY5 United States Patent METHODS OF MAKING NON-RIGID ROTATIVEABRASIVE STRUCTURES Theodore J. Miller, St. Paul, Minn., and Earl L.Gothier,

Detroit, Mich., assignors to Minnesota Mining & Manufactoring Company,St. Paul, Minn., a corporation of Delaware Original application November7, 1955, Serial No. 545,390. Divided and this application February 17,1958, Serial No. 715,802

3 Claims. (Cl. 51-497) The present invention relates to new and improvedrotative abrasive structures comprised of an annulus of radiallyextending juxtaposed flat sections of abrasive sheet material, tomethods of manufacturing the same and to novel methods by which thesestructures are employed in abrading and finishing operations. Thisapplication is a division of our copending application Serial No.545,390, filed November 7, 1955 and now abandoned.

In the grinding and finishing of metal articles of curved or irregularlyshaped surfaces, such as automobile accessories, preparatory to theplating or painting thereof, several different abrasive articles andprocedures have heretofore been employed. For example, abrasive set-upwheels, abrasive belts and sisal buffs have all been used. Of these, thefirst named has seen widest use. Each has particular advantagesrendering it suitable in abrading and finishing operations; yet each isendowed with one or more disadvantages which limit its practicalutility.

Abrasive belts have seen extended use in operations where it isdesirable to remove stock rapidly, particularly where fiat or nearlyfiat surfaces are being abraded. By their very nature, however, abrasivebelts are not very satisfactory where workpieces have extreme curvedsurfaces. Where surfaces of slight curvature are being abraded, beltsare occasionally used in conjunction with contact or back up wheelshaving special irregular peripheral shapes. However, such usenecessitates a specially shaped contact wheel for each type of articleabraded. Belts are further disadvantageous where employed to abradeworkpieces which have wide curved surfaces. The belt edges have atendency to gouge and scar the workpiece making special finishingoperations necessary to insure that gouge or scar marks which wouldappear after the article has been plated, painted, etc., are removed.

In most operations where articles of curved irregular contours are beingabraded and finished, abrasive setup wheels are most generally employedfollowed by a buffing operation. Set-up wheels are cloth buffing wheelsto the peripheral surfaces of which have been bonded abrasive grains.The grains are bonded to the surface of the cloth by means of anadhesive binder which has been hardened or set-up. A wheel having a hardrigid surface results. However, just prior to being used the abrasivecoat is hammered to break up the surface into discontinuous clumps ofabrasive and binder adhered to the cloth so as to render the abrasivecoating somewhat resilient and yieldable to the contours of theworkpieces. As can be readily seen, the hammering or breaking up of theabrasive coated surface to render the wheel suitable also reduces theuseful life of the wheel. In fact, in typical abrading operations suchset-up wheels must be replaced every 30-40 minutes. Costly work-stoppageand down time results which raises substantially the cost of abradingand finishing operations employing such wheels.

The use of sisal buffs, cloth buffing wheels containing layers of ropefibers, is also not uncommon. When sisal 2,843,469 Patented July 15,1958 'ice buffs are employed, abrasive compounds are added to thesurfaces of the buffs during the operations, and serve as the primaryabrasive component. Such operations are inconvenient, costly in thatspecial equipment is required to handle the abrasive compounds,inefficient and extremely messy.

The present invention provides novel improved structures which obviatedisadvantages heretofore known in the abrading and finishing art. Itprovides structures which accurately rapidly abrade workpieces havingextreme curved irregular surface contours while effecting fine finishesthereto, irrespective of workpiece dimensions. Yet the structures hereofare also convenient to handle, install and replace and are operatedwithout need of special operating equipment. In addition, the abrasivestructures have long useful abrading lives so as to decrease to aminimum the necessary costly down time in abrading operations. Ourinvention further provides novel methods whereby our abrasive structuresmay be utilized to the peak of their efficiencies, and also providesmethods whereby the novel structures may be manufactured uniformly,accurately and economically.

Our invention will now be more fully described in connection with hedescription of the accompanying illustrative drawings, wherein likecharacter references refer to corresponding parts in the several views,and in which:

Figure l is a plan view of an abrasive sheel flap section employed in anabrasive wheel structure of the present invention;

Figure 2 is an exploded view in perspective showing the manner in whichan abrasive wheel structure of the present invention, shown partly insection, is mounted for operation;

Figure 3 is a mid-section view of the assembly of Figure 2 which hasbeen employed in an abrading and finishing operation;

Figure 4 is a schematic view of a portion of an automatic abrading andfinishing operation employing an abrasive wheel structure of the presentinvention; and

Figure 5 is a perspective view, partially cutaway, of an alternativeabrasive wheel structure embodied in the present invention.

Referring now generally to Figures l3, a unitary abrasive wheelstructure is formed, in a manner hereinafter to be described, of anannulus of many radially extending juxtaposed fiap sections 10previously die-cut in the configuration shown in Figure 1 from coatedabrasive sheet material. Adjacent flap sections 10 in the annulus arefirmly rigidified and adhesively bonded together over a substantial area11 at the radially inner portions thereof, which area extends across theentire width of the sheet and for a substantial distance, at least about/4 inch, radially outward from the inner edge of the sections. Thus, theannulus is provided with a strong rigid reinforced inner rim. Theseveral fiap sections 10- are positioned such that the abrasive surfacesthereof extend in the same direction around the wheel structure with theabrasive surface of one section facing the back surface of the adjacentsection.

The generally rectangular flap sections 10 each have a pair of opposednotches l2 and 12a (Figure 1) extending inwardly from the lateral edgesnear one end thereof. A second pair of opposed notches l3 and 13aextends inwardly from the lateral edges of the fiap section adjacent thefirst mentioned notches 12 and 120, respectively, to a depth somewhatgreater than that of the latter. The portions of the flap sectionsextending between the notches l2 and 13 and between notch 13 and the endof the section terminate identically short of an extension line of thelateral edge of the flap section. Correspondingly, the similarprotrusions on the opposite edge of the flap section terminate short ofthe lateral edge extension. The notches 12 and 12a of the several flapsections align to define opposed outer circular grooves 14 and 14a,respectively, in the lateral surface of the annular structure near theinner periphery thereof; notches 13 and 13a similarly align to defineinner circular grooves 15 and 15a, respectively.

The abrasive wheel structure is conveniently mounted for rotation on andwith a shaft as shown particularly in Figure 3. A cylindrical hub 16,having an outer diameter slightly smaller than the inner peripheraldiameter of the abrasive annulus and a width equal to the width of thelatter at its inner periphery, is inserted into the center hole of theannulus. A flange 17, having a ring 18 extending laterally from the sidesurface at theouter edge thereof and a ring 19 of smaller diameter thanand concentric with ring 18 extending laterally from said surface, isaflixed one end of the hub 16 by means of bolts 20, the rings 18 and 19extending into and being snugly received by the grooves 14 and 15,respectively, of the abrasive wheel structure. The said rings preventradial expansion of the annulus during rotation due to centrifugalforces. Similarly, flange 17a, having laterally extending rings 18a and19a is affixed the other end of hub 16 with the said rings being snuglyreceived by the grooves 14a and 15a, respectively. When flanges 17 and17a are in position, their exposed side surfaces fit approximately flushwith the lateral surfaces of the abrasive wheel due to the previouslynoted configuration of the flaps 10.

In order to minimize stress concentrations in the structure duringoperation, the grooves in the structure, as defined by the notches inthe individual flap sections 10, and, correspondingly, the rings of theflanges l7 and 17a are rounded out.

A cylindrical bushing 21 extends through the flanges 17 and 17a and thehub 16 and terminates flush with the exposed surfaces of the flanges.The bushing 21 receives a partially threaded shaft 22, the entire wheelassembly being affixed thereon by means of a pair of internally threadedhexagonal-head nuts 23 and 23a which are turned onto the shaft 22 andbrought up tight against the flanges l7 and 17a.

A specific abrasive structure like that described is comprised of 850abrasive sheet flap sections having a width of 4 inches and a length of5 inches, the notches being positioned in the end one inch of the flaps.The abrasive sheet material consists of grit 180 coated abrasive sheetmaterial in which the abrasive particles are adhered to a drills-clothbacking sheet by cured phenol-aldehyde bond and sandsize adhesivecoatings. The annulus of radially extending flap sections has an outerdiameter of 16 inches and an inner diameter of 6 inches. Each of theseveral flap sections is rigidified at the inner end and rigidly andfirmly adhered to adjacent sections with a cured epoxide resincomposition'consisting of the reaction product of Bis-phenol A" andepichlorohydrin, having an epoxy number of approximately 192 grams perepoxide equivalent and a hydroxy number of 80 grams per hydroxyequivalent (sold under the trade name of Bakelite BR-l8774), acceleratedwith diethylene triamine, the ratio of resin to accelerator being 10:1.An area of the entirewidth of each flap section on each surface thereofwas covered with the adhesive for a distance of at least 96 inch fromthe radially inner end.

It has been found that the abrading action in our abrasive structureoccurs principally at the tips of the individual flap sections,particularly when operated at advanced speed as described hereinafter,rather than on the surface of bent over or flexed flap sections. Thetipedge of the individual flaps contact the workpiece surface while theflaps are at right angles thereto. It would be expected that in suchcase the rate of stock removal would be extremely low, it being wellknown that in highly eflicient coated abrasive belt operations the beltpasses in parallel contact with the workpiece surface. On the contrary,however, our novel structures demonstrate extremely high rates of stockremoval. Moreover, when the structures hereof are employed to abrade andfinish indentically shaped articles, such as occurs in automaticabrading operations, the peripheral surface actually takes the contourof the articles being abraded. This feature permits large areas ofirregularly shaped workpieces to be evenly abraded in a single pass. InFigure 3, the abrasive flap sections 10 of the abrasive structure areseen to have taken the contour 24 of a workpiece during an abrading andfinishing operation.

Due to the unique tip-grinding characteristics of our novel abrasivewheel structures the flap sections wear only at the tip-ends thereof.Thus, a fresh abrading surface is continually presented to theworkpiece; yet abrading life of our structures is remarkably long, aswill be specifically shown presently. Moreover, the wheels are usableuntil worn down to the rigid inner rim portions without substantialchange in abrading characteristics.

One application in which the structures hereof have seen extended use isshown in Figure 4, the automatic abrading and finishing of the broadside surfaces of automobile bumperguards being illustrated. An abrasivewheel assembly, or abrasive head 30, is mounted on a shaft 31, thelatter being rotatably aflixed the end of platform 32 and driven in thedirection of the arrow by suitable means such as an attached electricmotor, or a motor and belt assembly (not shown). Platform 32 ispivotally mounted about an axis 33 permitting the abrasive head to beraised and lowered. Since the weight of the abrasive head 30 isconsiderably more than the abrading force to be exerted, a counterweight34 slidably attached to the other end of the platform 32 decreases theforce exerted by the abrading head due to its own weight againstworkpieces, here bumperguards 35, which pass under and in contacttherewith. The abrading force may be varied by sliding the counterweight34 on the platform 32. Supports 36 carried by a conveyor 37, whichtravels in the direction shown by the arrow, support and retain thebumperguards 35 in position during the operation. In passing intocontact with, under and beyond the abrasive head 30, the forward edge ofbumperguards 35 engage the rotating wheel, and as the bumperguards 35advance, the wheel is raised, platform 32 being pivoted about axis 33,due to the upward force exerted thereagainst by the advancing increasingheight of the bumperguard surface. As the article passes under andbeyond the abrasive head 30. the latter is lowered again. A suitablestop, not shown, supports the platform with the head 30 in position forthe next cycle. Thus, the bumperguard 35 is contacted by the abrasivewheel over substantially its entire length.

The 16 inch diameter, 4 inch wide wheel structure above described wasassembled, the flanges being 8 inches in diameter, and employed withsimilar structures in the above described bumperguard abrading andfinishing operation. The counterweight 34 was adjusted such that theforce exerted by the wheel against the bumperguards was 12 pounds.Conveyor speed was such that bumperguards passed under the abrasive headat the rate of 600 per hour. Preliminarily, several bumperguards werepassed under the new wheel structure rotating at 1850 R. P. M. in orderto impart the surface contour of the bumperguards thereto. After about 5minutes time, during which about 50 articles passed in contact with thewheel, the wheel periphery had taken the contour of the guards such thatnearly the entire side surfaces of the bumperguards were abraded in asingle pass.

When rotated at a speed of about 1850 R. P. M.. the abrading life of thecontoured abrasive wheel structures was found to be about 3000-4000bumperguards. That is, after abrading about this number, the flapsections on the wheel were worn down nearly to the rigid inner rimportion of the wheel. This necessitated about 5 minutes down time every5-6.7 hours for replacement of the wheel. Such an abrading life ishighly satisfactory compared to the minutes down time required every40-45 minutes for set-up abrasive wheels in identical operations. Yet,surprisingly, we found that upon increasing the retative speed of ourabrasive structures about percent, or to about 2200 R. P. M., where itwould be expected that abrading life would decrease slightly, the usefullife of each wheel structure increased many-foldto about 10,00012,000bumperguards. Replacement of a wheel was then required only every 17-20hours. Moreover, the finish imparted to the bumperguards was seen tohave been improved considerably; at the advanced speed the finishimparted by the grit 150 wheel approximated that of a grit 180 abrasivebelt whereas at the lower rotative speed the finish was similar to thatimparted by a grit 150 abrasive belt. Rate of stock removal was found tobe extremely high, three of our structures effectively replacing in manyinstances four prior art abrasive set-up wheels of like abrasive grade.

The rotative speed range at which the abrading life of the structuresincreased so remarkably could be visually ascertained. At the 1850 R. P.M. speed, the abrasive articles were seen to emit threads and pieces ofthe abrasive sheet flap sections of which the wheel structures werecomposed. This shredding of the individual flap sections occurredparticularly as the bumperguards initially contacted the wheels.However, when the rotative speed was increased the shredding graduallydiminished and at 2200 R. P. M. and beyond, no direct visual evidence ofshredding could be seen.

Although the above specific example demonstrates abrasive wheelstructures hereof of particular dimensions and shows them being employedin a particular use, the dimensions of our articles need not be confinedto those above shown. Nor are the uses in which spectacular results areexhibited limited to that above shown. In fact, the abrasive articles ofthe present invention have been employed with similar success in manyabrading and finishing operations. For example, they have been employedin grinding and polishing of jet aircraft engine blades in whichextremely high precisicr is necessary, in the removing of rough scaleresulting on iron and steel pieces from rough forging and particularlyon fiat plates (which, incidentally, is accomplished only poorly or notat all with abrasive belts), in the p lishing of glass and for manyother applications.

The rotative speed range at which the abrading life of these abrasivestructures increases so surprisingly, varies according to the materialsof which the abrasive structure is formed, e. g., stiffness of theabrasive sheets, wheel dimensions, the extent to which the flap sectionsare rigidified in the radical direction and adhered to ad jacent flaps,etc., and the abrading conu ions in which they are employed. Generally,it can be stated that the critical range is lower in a given operationwhere a large wheel with a relatively large inner diameter is employedand/or where relatively stiff abrasive sections are employed than in theconverse case. However, in each instance the range at which thecharacteristics undergo the change may be visually determined by thewheel shredding observed. Where rapid wear by shredding may be observedat rotative speeds below the transition range, particularly where aworkpiece is initiallv forced against the wheel in a nonradial directionsuch as occurs in automatic operations, no such shredding is seen atrotative speeds above the transition range. The transition does notoccur instantaneously. It does, however, occur over a relatively slightincrease in rotative speed, generally over an increase in rotative speedby only a few hundred R. P. M.

The use of our novel structures has permitted extreme economic savingsin the abrading and finishing industry, primarily in the abrading andfinishing of automotive parts and accessories and in similar types ofoperations. For the first time commercially has been provided a rotativeabrasive article capable of quickly rapidly and accurately abradingworkpieces of irregular contour while imparting a fine superior finishthereto, yet which has an abrading life many times that of abrasivearticles previously employed for such operations.

We are aware, in pointing out our invention, that abrasive wheels formedof radially extending flap sections of abrasive sheet material have beenknown for many years, indeed since before the turn of the century. Morerecently, Leggett Patents Nos. 2,651,894 and 2,678,523 have been issued,covering modified forms of abrasive flap wheels. Such wheels have proveneffective under the conditions and for the purposes for which they weredesigned. Significantly, however, they have not been made available inwidths much, if any, beyond one or two inches; they are restricted touse at relatively low rotative speeds; and they do not provide the noveltype of contourable tip-abrading now made possible with the novelstructures of the present invention.

The 16 inch diameter wheel structure containing 850 flap sections (gritpreviously described was prepared as follows: The previously die-cutflap sections 10 were assembled in face-to-back relation in an elongatechannel member of U-shaped cross section. The flap sections werearranged with the ends adjacent the notches extending upwardly. The rowof flaps was then compressed together. The compressive force was thenreleased somewhat permitting the fiap sections to spread apart slightlyand a one-half inch wide strip of pressure sensitive adhesive coatedmasking tape was applied along each edge of the top surface of the blockof slightly spread sections. Approximately 23 ounces of the previouslyprepared syrupy liquid epoxide resinous adhesive with acceleratorblended in, having a useful pot-life of about l520 minutes, was thenapplied uniformly to the exposed surface of the block between the tapestrips and allowed to penetrate between the individual flap sections.The block of sheets was then compressed under a pneumatic ram force of700 pounds. Excess resin was wiped from the surface of the compressedblock of flap sections. The strips of tape were then removed leavingedge surfaces which had not been adhesively wet. A pair of strips of themasking tape, the adhesive surfaces of which had been coated with arubber based air-drying cement, were then positioned where the formerstrips had been. The block of flap sections was retained under thecompressive force for about 10-15 minutes to permit the cement to dry atwhich time the pressure was released.

The block of flap sections was then removed from the channel, theindividual flap being adhered to and bound by the tape strips, andmanipulated into an annulus by bringing the end flap sections togetherwith the tape strips on the inside. An 8 inch diameter steel formingring was then temporarily driven into the radially outer lateral grooveon each side of the structure to perfect the uniform annular shapethereof and compress the radially inner portions of the flap sectionstogether. The two strips of tape were then removed from the innerperipheral surface. While the annulus was laid on a side, additionaladhesive resin was poured into the radially inner groove on the exposedsurface to insure adhesive impregnation entirely across the structure.Simultaneously, adhesive resin was painted over the entire innerperipheral surface. After the resin poured in the groove had penetratedbetween the fiap sections and disappeared from view. the structure wasinverted and the adhesive application repeated on the other side. About23 ounces of additional adhesive resin was utilized in these latterapplications, making the amount of adhesive employed in the structuretotal about 5 ounces. The wheel was then stored at room temperature for12 hours while the adhesive resin cured to rigidly unify the structureand adhere adjacent flap sections in a rigid reinforced inner rirnportion. The temporary steel forming rings were then removed, thegrooves were cleaned out with coated abrasive paper to remove excessresin and permit close fit of the flanges 17, 17a, and the article wasboxed ready for shipping as a unitary article of commerce to be latermounted for operation on a hub assembly.

The amount of adhesive resin employed was sufficient to adequately bondthe flap sections without having adhesive excess flow from the structureduring application. However, the amount of adhesive necessary toadequately bond the flap sections and form the rigid inner rim portionwithout adhesive excess will vary for structures of differentdimensions, abrasive grit size, etc., the five ounce quantity shownbeing merely that required in the specific illustrative example.

The rigid inner structure provided in the structures hereof by theunifying adhesive is particularly important in preventing flap sectionsfrom being axially buckled or compressed upon subjection to severeworking stresses. As was previously mentioned, the unifying adhesiveextended radially at least about 5 inch from the inner periphery andcontinuously across the width of the wheel structure of the precedingspecific example. Near the wheel sides, penetration was somewhat greaterthan 56 inch due to that adhesive resin which had been added fromlateral grooves as is shown in Figures 2 and 3. We have found that theminimum radial depth to which the unifying adhesive must penetrate inorder to sufficiently rigidity the structure is about inch. Where thepenetration is less than about this depth a weak spot exists in thestructure at which point individual flap sections can buckle duringoperation causing failure of the structure. This is particularlyimportant where wide wheel structures, that is, two inches wide andwider, are to be employed. Where each flap section is rigidified asabove stated by the adhesive, the necessary rigidity is present in theinner rim portion of the assembled wheel even though a few flap sectionsare not adhered to adjacent sections on both surfaces thereof, in whichevent the wheel structure is in more than a single unitary segment. Forexample, even where a structure has been broken into one or moresegments in transmit it may be assembled on a shaft (the centripetallyreinforcing side members, e. g., ring containing flanges, holding thesegments together) and safely operated at high speeds.

The rigid inner rim portion of our abrasive wheel structures may bestill further rigidified by adhesively imbedding one or more annularreinforcing inserts, made, for example, of glass fiber reinforcedplastic, in the interior of the inner rim portion. This may be done byforming identically positioned small notches in the individual flapsections at the fiap ends which will become the inner periphery of thewheel structures. The notches align to define a groove into which theannular reinforcing insert is positioned as the structure is formed intoan annulus. When firmly rigidly adhered in position, the reinforcinginsert structurally cooperates with the rigid inner rim portion to evenmore firmly rigidify our wheel structures. It is to be understood,however, that such inserts are to be used only in conjunction with, notas a substitute for, the rigid inner rim portion formed of adhesivelyrigidified adhered fiap sections. During the initial adhesive resinapplication, such end grooves may be filled with resin and thus servethe additional function of facilitating deep penetration of the resinaround the grooves.

Other rigidifying and unifying resins than cured cpoxide resincompositions may be employed in the abrasive structure hereof. Forexample, resins which cure to a strong rigid adherent state from aliquid stage such as polyester resins. alkyd resins, phenolic resins andother similar adhesive materials well known to the art are also useful.

It is not necessary that two grooves be present on the lateral surfaceof our abrasive wheel structures in order to provide means for theprevention of radial expansion due to centrifugal forces. Lesser orgreater numbers of grooves may be employed; in fact, no grooves need bepresent at all. In Figure 5, a wheel structure is shown having nolateral grooves. The annulus formed of radially extending juxtaposedabrasive flap sections 40 rigidified and adherently bonded together intoa rigid 'inner rim section by rigid unifying adhesive 41 is providedwith a depression 42 at the inner portion of each lateral surface.Centripetal reinforcing washers 43 (only one shown) which may consist ofglass reinforced plastic, metal or other substance of high tensilestrength, are adhered to the lateral surfaces of the inner rim portionin the depression 42 by means of an adhesive of high shear strength. Thestructure is then mounted on a hub assembly and placed, either singly ormultiply, on a shaft for rotation. Any suitable adhesive is employed, inmany instances this adhesive being the same as that employed for therigid unifying adhesive 41.

Having now fully described our invention, it is to be understood thatthe various specific examples shown are for the purpose of illustration,not limitation, and that the scope of the invention is intended to belimited only by the disclosure as a whole, including the appendedclaims.

We claim:

1. In the method of forming an abrasive wheel comprised of an annulus ofjuxtaposed radially extending flap sections of abrasive sheet materialhaving opposed notches therein which align to define opposed lateralgrooves adjacent the inner periphery of said annulus and whereinadjacent flap sections are rigidified and firmly rigidly adhesivelybonded together over a substantial inner end area to form a rigidreinforced inner rim portion in said structure, the steps comprisingmanipulating into an annulus a block of said notched flap sectionsarranged in superposed face-to-back relation, said block beingtemporarly bound together at the end portions of said flap sectionsforming the inner peripheral portion of said annulus by a flexibleholding member which is affixed to said block, inserting a circularforming member into a groove in each of said lateral surfaces to perfectthe shape of said annulus, said sections each being provided with acoating of a liquid curable adhesive resin on each side over asubstantial area adjacent the radially inner ends thereof, and curingsaid resin to a hard firm state.

2. In the method of forming an abrasive wheel comprised of an annulus ofjuxtaposed radially extending flap sections of abrasive sheet materialwherein adjacent flap sections are rigidified and firmly rigidlyadhesively bonded together over a substantial inner end area to form arigid reinforced inner rim portion in said structure, the stepscomprising manipulating into an annulus a block of superimposedidentically shaped flap sections of abrasive sheet material temporarilybound together in faceto-back relationship 'by a flexible tape stripadhered to one end of said sections, said sections each having a coatingof a liquid curable adhesive resin on each side thereof over asubstantial area adjacent said end and further having opposed notches inthe lateral edges thereof adjacent said end which align to form opposedcircular grooves in the lateral surfaces of said annulus, temporarilyinserting a circular forming ring into a groove in each of said lateralsurfaces to perfect the shape of said annulus, curing said resin to arigid hard firm state and removing the rings.

3. A method of forming an abrasive wheel comprised of an annulus of manyjuxtaposed radially extending flap sections of abrasive sheet materialwherein adjacent flap sections are rigidified and firmly rigidlyadhesively bonded together over a substantial inner end area to form arigid reinforced inner rim portion in said structure, said methodcompising forming a loosely compacted block of superimposed identicallyshaped fiap sections of abrasive sheet material each of which has twopair of opposed notches in its lateral edges near the upper end thereof,applying a liquid curable adhesive resin to the upper surface of saidblock and allowing said resin to penetrate between individual flapsections, compacting said block, adhering a flexible tape strip alongthe upper surface of said block, manipulating the taped block with saidtape on the inside into an annulus by bringing the end flap sectionstogether, said annulus having two pair of opposed circular grooves inthe lateral surfaces thereof defined by the alignment of said notches,temporarily inserting a circular forming ring into one of said groovesin each of said lateral surfaces to perfect the shape of said annulus,and flowing additional resin into the remaining grooves and allowing itto penetrate between individual sections to complete the resinouscoating on said flaps over a substantial radial distance from the innerend thereof and '10 across the entire width of the sheet, curing saidresin to a rigid hard firm state and removing the rings.

References Cited in the file of this patent UNITED STATES PATENTS UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No; 2,843,469 July15, 1958 Theodore J. Miller et a1.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 2, line 24, for 'he" read the column 5, line 51, for "radical"read radial column '7, line 67, for "structure" read structures column8, line 70, for "compising" read comprising Signed and sealed this 12thday of May 1959.

' (SEAL) Atteat:

KARL H. AXLINE ROBERT C. WATSON Attesting' Officer Commissioner ofPatents

1. IN THE METHOD OF FORMING AN ABRASIVE WHEEL COMPRISED OF AN ANNULUS OFJUXTAPOSED RADIALLY EXTENDING FLAP SECTIONS OF ABRASIVE SHEET MATERIALHAVING OPPOSED NOTCHES THEREIN WHICH ALIGN TO DEFINE OPPOSED LATERALGROOVES ADJACENT THE INNER PERIPHERY OF SAID ANNULUS AND WHEREINADJACENT FLAP SECTIONS ARE RIGIDIFIED AND FIRMLY RIGIDLY ADHESIVELYBONDED TOGETHER OVER A SUBSTANTIAL INNER END AREA TO FORM A RIGIDREINFORCED INNER RIM PORTION IN SAID STRUCTURE, THE STEPS COMPRISINGMANIPULATING INTO AN ANNULUS A BLOCK OF SAID NOTCHED FLAP SECTIONSARRANGED IN SUPERPOSED FACE-TO-BACK RELATION, SAID BLOCK BEINGTEMPORARLY BOUND TOGETHER AT THE END PORTIONS OF SAID FLAP SECTIONSFORMING THE INNER PERIPHERAL PORTION OF SAID ANNULUS BY A FLEXIBLEHOLDING MEMBER WHICH IS AFFIXED TO SAID BLOCK, INSERTING A CIRCULARFORMING MEMBER INTO A GROOVE IN EACH OF SAID LATERAL SURFACES TO PERFECTTHE SHAPE OF SAID ANNULUS, SAID SECTIONS EACH BEING PROVIDED WITH ACOATING OF A LIQUID CURABLE ADHESIVE RESIN ON EACH SAID OVER ASUBSTANTIAL AREA ADJACENT THE RADIALLY INNER ENDS THEREOF, AND CURINGSAID RESIN TO A HARD FIRM STATE.